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   "source": [
    "# Copyright 2014 Brett Slatkin, Pearson Education Inc.\n",
    "#\n",
    "# Licensed under the Apache License, Version 2.0 (the \"License\");\n",
    "# you may not use this file except in compliance with the License.\n",
    "# You may obtain a copy of the License at\n",
    "#\n",
    "#     http://www.apache.org/licenses/LICENSE-2.0\n",
    "#\n",
    "# Unless required by applicable law or agreed to in writing, software\n",
    "# distributed under the License is distributed on an \"AS IS\" BASIS,\n",
    "# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.\n",
    "# See the License for the specific language governing permissions and\n",
    "# limitations under the License.\n",
    "\n",
    "# Preamble to mimick book environment\n",
    "import logging\n",
    "from pprint import pprint\n",
    "from sys import stdout as STDOUT"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# Example 1\n",
    "class Field(object):\n",
    "    def __init__(self, name):\n",
    "        self.name = name\n",
    "        self.internal_name = '_' + self.name\n",
    "\n",
    "    def __get__(self, instance, instance_type):\n",
    "        if instance is None: return self\n",
    "        return getattr(instance, self.internal_name, '')\n",
    "\n",
    "    def __set__(self, instance, value):\n",
    "        setattr(instance, self.internal_name, value)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# Example 2\n",
    "class Customer(object):\n",
    "    # Class attributes\n",
    "    first_name = Field('first_name')\n",
    "    last_name = Field('last_name')\n",
    "    prefix = Field('prefix')\n",
    "    suffix = Field('suffix')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Before: '' {}\n",
      "After:  'Euclid' {'_first_name': 'Euclid'}\n"
     ]
    }
   ],
   "source": [
    "# Example 3\n",
    "foo = Customer()\n",
    "print('Before:', repr(foo.first_name), foo.__dict__)\n",
    "foo.first_name = 'Euclid'\n",
    "print('After: ', repr(foo.first_name), foo.__dict__)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# Example 4\n",
    "class Meta(type):\n",
    "    def __new__(meta, name, bases, class_dict):\n",
    "        for key, value in class_dict.items():\n",
    "            if isinstance(value, Field):\n",
    "                value.name = key\n",
    "                value.internal_name = '_' + key\n",
    "        cls = type.__new__(meta, name, bases, class_dict)\n",
    "        return cls"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# Example 5\n",
    "class DatabaseRow(object, metaclass=Meta):\n",
    "    pass"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# Example 6\n",
    "class Field(object):\n",
    "    def __init__(self):\n",
    "        # These will be assigned by the metaclass.\n",
    "        self.name = None\n",
    "        self.internal_name = None\n",
    "    def __get__(self, instance, instance_type):\n",
    "        if instance is None: return self\n",
    "        return getattr(instance, self.internal_name, '')\n",
    "\n",
    "    def __set__(self, instance, value):\n",
    "        setattr(instance, self.internal_name, value)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# Example 7\n",
    "class BetterCustomer(DatabaseRow):\n",
    "    first_name = Field()\n",
    "    last_name = Field()\n",
    "    prefix = Field()\n",
    "    suffix = Field()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Before: '' {}\n",
      "After:  'Euler' {'_first_name': 'Euler'}\n"
     ]
    }
   ],
   "source": [
    "# Example 8\n",
    "foo = BetterCustomer()\n",
    "print('Before:', repr(foo.first_name), foo.__dict__)\n",
    "foo.first_name = 'Euler'\n",
    "print('After: ', repr(foo.first_name), foo.__dict__)"
   ]
  }
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